This invention relates to a pneumatic tire and a method of making a pneumatic tire.
It is conventional in the art to build a pneumatic tire having an inner liner comprised of a rubber (usually halobutyl) which has low air permeability in order to help maintain tire inflation and to prevent gases from migrating into the carcass plies and belt plies of the tire. In general, because of the purpose for which it is used, rubber used as an inner liner is soft and has a relatively low tear strength and modulus compared to other types of rubber used in a tire. Accordingly, in the prior art, inner liner rubber was limited to use in non-stress areas of the inner tire between the tire beads.
In the conventional building of the tire, toe guards are placed in an overlapping position on the inner liner prior to application of the carcass plies, and are folded over the beads together with the carcass plies to provide a tough, tear resistant material over the outside of the beads and the carcass plies for contact with the rim. Toe guards conventionally comprise a bias fabric which is coated and impermeated with a tough, tear resistant rubber compound. The bias cut of the fabric permits expansion of the material when it is wrapped around the tire bead in the construction of a tire. Providing tough, tear resistant toe guards protects the tire in the rim area during mounting and dismounting and helps prevent leaks from developing around the rim.
Providing toe guards in this manner has the disadvantages that: additional compounding is required for a separate composition for the toe guard; additional application steps are required to apply the toe guard in an overlapping relationship on the edges of the inner liner; and the toe guard, because of its gauge, may permit air to be trapped between the inner liner, and the carcass plies. Also, since the inner liner does not extend over the beads, air permeability in this region of the tire may be greater than that observed for the rest of the tire.
It is an object of the present invention to provide a method of building a tire and a tire made thereby in which the toe guards and inner liner are together in one substantially integral structure. Using such a structure reduces the number of building steps required, and accordingly reduces the expense of building a tire, while maintaining superior physical properties.
Other objects of the invention will be apparent from the following description and claims.